Floor Deflection (HELP CX) [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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02-22-2008, 07:17 PM
I know there are numerous folks out there who have a very responsible knowledge of this particular phenom. However, I am not one of them.
While searching the archives I found a reference from CX about a "deflection" calculator which "Bob" created for the gang. I was not able to locate said calculator.

I would have quoted CX directly, however, my lack of knowledge about floor deflection is only surpased by my lack of knowledge about computers (oh, and astro-physics).

Any way does this calculator exist and is it as easy to read as the instruction manual for a framing square?

Or a much easier approach -

Can I set floor tile on a subfloor which is constructed with 4 x 6" beams on 48" centers, covered with 1 1/4" ply. (Yea, we still have that in the NW).

So it has been awhile since CX has yelled at me, thought I would give him another chance.

Thanks for the assist.


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02-22-2008, 07:23 PM

Look on the bottom row of the dark blue bar. There is Deflecto right between Liberry and Calculator. Pretty smart of me, for a girl that is. :D

02-22-2008, 07:25 PM
Deflecto is inna blue bar near the top of the page. Says "Deflecto" in white. Self explanatory. Easier than the instructions on a framing square.

But it won't help you at all with your current project.

Short answer, no.

But if your beam supports are adequately spaced and if you were to properly add another half-inch layer of plywood, I think you might could do ceramic tile. Might take 3/4" plywood. I ain't equipped to make that calculation for you, unfortunately.

I'll be happy to yell at you though, if you like. What have you done this time? :D

Besides post your thread inna Mud Box? :rolleyes:

My opinion; worth price charged.

02-22-2008, 07:26 PM
Mike, as Kathleen mentioned, there is a link button that says DEFLECTO in the blue bar directly above this thread. Or, you could just click on this (http://www.johnbridge.com/vbulletin/deflecto.pl) link too. :)

02-22-2008, 07:35 PM
I am duly chastised!

I knew that I would make your day CX!



02-22-2008, 07:43 PM
One more question before I get a glass of warm milk, my teddy bear and pillow and call it a night.

On the bottom of the "deflecto" calculator it suggests that JB has engineers who would be estatic to calculate my (not me personally you understand) deflection. If this is indeed true what additional info would I need. Just length of the floor joists?

Thanks again.


02-22-2008, 07:49 PM
Don't nobody really wanna calculate your joist, Mike. That was all printed years ago when we got only nice, friendly visitors. :D

The missing information is the spacing of the supports under your beams.

Injineer Bob has done the calculations for these Left Coast floors, but only with the much more traditional 2x6 T&G carplank flooring. That flooring, with a half-inch plywood over it is known to be sufficient for ceramic tile. But not natural stone.

Whether your 1 1/4" plywood with the same half-inch ply over it would also be satisfactory I cannot say.

I'm sure Injineer Bob will come by here to verify one way or the other, so long as we don't tell him in advance who's floor it is, eh? :)